When I have to go through the horror of buying tracks on Itunes because I am in Canada and Amazon is blocked from selling MP3s here, I suffer for an hour installing Itunes, logging in, buying the tracks, and then removing Itunes ...... in the end I get M4a music files.

I usually just convert them to MP3 because raw tagged Itunes M4a files randomly just don't play in MM4. MP3s never do this.

I happens maybe 1 in 40 attempts to play a M4a, and generates a "Codec not Found" error message. I can click on that exact same track 1 second later and it plays perfectly.

I did at one time have the codec pack installed but I removed it a long time ago.